The next iteration involved check-boxes reading 'I'm not a robot' . This is the simplest option to integrate with and only requires two lines of HTML to render the checkbox.

'Lying' robot beats website security system by ticking the 'I am not a robot' box before 'smiling' at the camera Robotic arm does the Completely Automated Public Turing Test to tell Computers and ...

What is the purpose of the ‘I’m not a robot’? How does the reCAPTCHA work? Why do some websites check if you are a robot? Why does Google keep checking I’m not a robot? Can AI solve CAPTCHA?